1. Field
The invention relates to a method and a receiving circuit for compensating for an IQ mismatch.
2. Background
FIG. 1 is a diagram illustrating a conventional receiving circuit. Referring to FIG. 1, the receiving circuit includes an IQ mixer 10, a quadrature signal generator 11, a first and a second variable gain amplifiers 20 and 21, a first and a second band pass filters 30 and 31, a first and a second analog-to-digital converters 40 and 41, and a base band converter 50. A received RF signal is converted to an intermediate frequency signal by the IQ mixer 10. The intermediate signal is then passed through the first and the second variable gain amplifiers 20 and 21 and the first and the second band pass filters 30 and 31, and is converted to a digital signal by the first and the second analog-to-digital converters 40 and 41. The digital signal is then converted to a base band signal by the base band converter 50.
Since the conventional receiving circuit shown in FIG. 1 does not impose an image problem ideally, the conventional receiving circuit is advantageous over a heterodyne type receiving circuit that converts a received RF signal to an intermediate frequency signal and then the intermediate frequency signal to a base band signal without using an IQ mixer. In addition, since the conventional circuit shown in FIG. 1 does not impose 1/f noise and DC offset problems, the conventional receiving circuit is advantageous over a direct conversion receiving circuit that converts a received RF signal to a base band signal using an IQ mixer. The conventional receiving circuit shown in FIG. 1 is gaining popularity due to these advantages.
However, the conventional receiving circuit has various disadvantages. For example, a real IQ mixer has an IQ mismatch. That is, the IQ mixer has a gain error generated because amplitudes of an in-phase (J) signal and a quadrature signal (Q) signal are not exactly the same, and a phase error generated because a phase difference between phases of the in-phase signal and the quadrature signal is not exactly 90°. When the received RF signal is converted to the intermediate frequency signal using the IQ mixer having the IQ mismatch and the intermediate frequency signal is then converted to the base band signal, an image is not completely removed, which can result in a degradation of a performance of a receiver.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.